Alcohol or ethanol affects the human nervous system by inhibiting signals between the brain, nerve endings and spinal cord. When people drink, their bloodstream absorbs the alcohol and nervous system functions slow down dramatically--this is the "buzz" or numbness people commonly feel after drinking. Alcohol affects the body much in the same way a sedative would, but it does not go through regular digestion, as is the case with a pill, like a sedative, for example. It goes straight to the bloodstream. This is what makes alcohol so dangerous--in some respects--if someone drinks too fast, the alcohol could virtually paralyze an organ completely.
The human body basically has two systems--voluntary and involuntary. The voluntary system controls your muscles, for example, while the involuntary or autonomic nervous system controls how fast or slow your organs can operate. It also controls your breathing and heart rate. Normally, electrical signals get sent from the brain to the body which basically regulate how a person breaths. If a person has some sort of preexisting medical condition, this process may be some what inhibited already. Again, a person has no control over how this portion of their nervous system functions, so when you drink excessively, the brain cannot properly interpret those electrical signals and a person might start shallow breathing or even stop breathing entirely.
Long and short-term effects
The long and short-term effects of alcohol on the nervous system depends on the quantity of alcohol consumed and for what duration. The effects also change overtime, as well depending on the level of tolerance a person builds up. This again, can also change over time, too. Human cells become less permeable to alcohol if a person drinks for an extended period of time. This means they literally become thicker. A healthy nervous system depends on healthy cells. If cells do build up a resistance to alcohol, a person is less able to fight infection and a number of serious problems can result. Stroke, heart attack and even dementia can be the result of alcohol's affect on the nervous system.